The present invention relates to providing power for accessories of a luminaire, and more particularly to extracting DC power from a lamp power signal supplied from a phase angle dimmer.
Luminaires for theatrical and architectural applications are provided with power by phase angle dimmers so that the lamps of the luminaires can be dimmed, or operated at variable, selected light levels. Phase angle dimmers for this purpose are well known, and typically include solid state switches such as SCRs for interconnecting an AC power source to a lamp load. AC voltage from the source is sinusoidal. A phase control circuit renders a solid state switch conductive at a point during a half cycle of the sinusoid, the point being selected to supply to the lamp a lamp operating pulse having a desired quantity of power in order to produce a desired level of light.
Although a luminaire can have a dedicated, internal dimmer, the typical approach in multiple luminaire applications is to provide centralized dimmers providing power through cabling extending to the distributed luminaires. Centralized dimmers are generally preferred because multiple luminaires can be supplied form a single dimmer, because centralized dimmers can be commonly controlled and because of efficient power distribution.
Systems including luminaires and phase angle dimmers are in widespread use and have been successfully employed for controlling variable light levels in many applications. There is an increasing desire to supplement dimming effects provided by luminaires with other variable parameters provided by accessories and automation. For example, it may be desirable to add mechanized devices such as color scrollers or color wheels or gobo wheels or the like to a dimmer powered luminaire. It may be desirable to provide a luminaire that can be moved by motors incorporated into the mount of the luminaire so that the beam of light from the luminaire can be aimed with pan and tilt motions. A luminaire may be provided with other accessory mechanisms such as a zoom lens, an iris or a shutter system.
Such accessories require power to operate. The motors used for automation and accessories are typically energized by low voltage DC power. The power supplied by dimmers for lamp energization is in the form of a series of lamp operating pulses having a frequency dependent on the AC line frequency. The pulses may be at, or at a multiple of, the line frequency depending on the dimmer system. The motors typically used for accessories cannot be powered directly from the dimmed power supplied for the lamp of a luminaire. Consequently, in known centralized dimmer systems, additional power cables are used to supply DC power for operation of accessories. A luminaire in this type of system is connected to one cable system providing lamp power from a dimmer and another independent cable system providing accessory power. This is an expensive and complex arrangement, particularly in view of the fact that a large number of luminaires may be used in any particular installation.
Another disadvantage of the need for independent accessory power supply wiring is encountered when retrofitting existing dimmer controlled systems where luminaires and light power cabling have been previously installed. If it is desired to add powered accessories to a previously installed system, it can be expensive and difficult to add a new, additional cable system for powering accessories.
To overcome the problems resulting from the need for separate cabling systems for lamp power and accessory power, it would be desirable to extract accessory power from the lamp power provided to the luminaire by a phase angle dimmer.
One potential difficulty with an accessory power extraction approach is that accessories used with luminaires have variable power requirements. For example, a motor for moving a luminaire to aim a light beam could draw little or no power when the luminaire is stationary but would draw an increased amount of power when the luminaire is moving. Similarly, with other types of powered luminaire accessories, the requirement for power can vary over time. If accessory power in varying amounts is extracted from the power supplied by a dimmer for lamp enerigation, the brilliance of the light emitted by the lamp of the luminaire could also vary. Light level variations due to powering of accessories are distracting, unattractive and undesirable.
Another potential difficulty is that the accessory power extracted from the lamp power from the dimmer must be sufficient to operate the accessory even when the lamp is off. But if the accessory and the lamp are supplied simultaneously, the power level needed for operation of the accessory could be so large that the lamp is powered to a visible state. This is undesirable because the lamp must be capable of being placed in an off state, or a filament preheat state, and even during this state, accessory power must remain available.
Another requirement is that the lamp should be capable of being powered to full brilliance. If accessory power is extracted from lamp power, this should be accomplished in such a way as not to decrease power in the full on state.
A primary object of the present invention is to extract accessory power from the lamp power provided by a phase angle dimmer for powering luminaire accessories without the need for additional DC power cables and without degrading lamp performance. Other objects are to provide a method and system for extracting accessory power over a range of accessory power loads while preserving the ability to operate a lamp at selected light levels from an off condition to a full power level; to provide a method and system for extracting accessory power that permits the lamp to operate in an off or preheat state; and to provide a method and system for extracting accessory power that permits the lamp to operate at full brilliance.
In brief, in accordance with the invention there is provided a power supply system for a luminaire having a lamp and having a powered accessory with varying power requirements. The power supply system includes a phase control dimmer with a solid state switch providing lamp operating pulses and having an output. An accessory power supply is connected between the dimmer output and the powered accessory. A lamp supply circuit branch is connected between the dimmer output and the lamp for transferring power from the lamp operating pulses to the lamp.
In brief, in accordance with the invention, there is provided a method for extracting power for luminaire accessory operation from lamp operating pulses supplied to a luminaire by a phase angle dimmer. The method includes supplying the output pulses from the phase angle dimmer to the input of an accessory power supply circuit. The output from the accessory power supply circuit is applied to a luminaire accessory having variable power requirements. The output pulses from the phase angle dimmer are delivered to the input of a lamp controller. The output from the lamp controller is furnished to a lamp of the luminaire. The transfer of the output pulses from the phase angle dimmer control to the lamp is regulated by operation of the lamp controller.